Hollow blades for turbines and the like



June 14, 1960 1.. 1. DENNIS HOLLOW BLADES FOR TURBINES AND THE LIKE Filed 001. 11, 1956 2 Sheets-Sheet 1 l 3 M 8 w 221M 111 1111 w 2 6 k 1 M I III 1.1.4 70 B HMU B a 24 INVENTOR LEONARD J. Deums June 14, 1960 L. J. DENNIS 2,940,726

HOLLOW BLADES FOR TURBINES AND THE LIKE Filed Oct. 11, 1956 2 Sheets-Sheet 2 INVENTOQ. LeoNnao J. DENNlS BY M, (2%,

A-r Team- 17 United States PatentOfice HOLLOW BLADES FOR TURBINES AND THE LIKE Leonard J. Dennis, Carpenders Park, England, assignor to D. Napier & Son Limited, London, England, a company of Great Britain Filed Oct. 11, 1956, Ser. No. '615,271

Claims priority, application Great Britain Nov. 8, 1955 '5 Claims. (Cl. 253-77) This invention relates to hollow blades for turbines and the like, which expression is intendedtoinclude both turbines and rotary compressors, the blades being either rotor blades or stator blades. However, as the invention can be used to the best advantage in blades for turbine rotors the invention will be described more particularly in relation to such blades.

Hollow blades for turbines, particularly gas turbines in which high temperature gases are employed, are known to have; several advantages over solid blades. In the first place, it is possible to cool them by circulating a cooling medium through the hollow interior of each blade. than a solid blade of similar cross-section, thereby reducing the centrifugal loading on the rotor. Diflicul-ty has been experienced, however, in providing satisfactory means for attaching hollow blades to the rotor. It is an object of the present invention to provide a hollow blade for a turbine or the like which is attached to its mounting in an improved manner.

-A blade according to the present invention comprises a root part shaped to fit into a groove in a member (e.g. a turbine rotor) on which the blade is to be mounted, a hollow blade part made from sheet material (which expression embraces both flat sheet and thin wall tubes, which need not be of uniform thickness) attached at one end to the root part and having an aerofoil cross-section for a substantial portion of its length and a transition portion of varying cross-section between the aerofoil portion and the end attached to the root part, and a platform part, which fits around the hollow blade part where the aerofoil portion joins the transition portion such that when several such blades are assembled together as a blade ring the platforms abut to form a partition between the blade channels defined by the said aerofoil portions of the blades and the transition portions of the blades.

Thus, in the case of a gas turbine for instance, the only parts of the blades exposed to the hot gases passing through the blade ring are the aerofoil portions andthe surfaces of the platforms. The gases do not come into contact with the transition portion, which not only reduces the risk of harmful turbulence or eddies being set up in the gas stream, but also keeps the hot gases away from the root parts of the blades and the rotor disc.

Conveniently, the platform part is an assembly of sheet metal pieces, for instance stampings and pressings. Portions of the platform part extend downwards towards the root part and are attached thereto to hold the platform part in the correct position on the blade. These downwardly-extending portions constitute front and rear walls for the transition portion. Their extremities are secured, as by welding or brazing, to front and rear surfaces of the root part.

The root part is made from solid material, for instance as a forging, and may have any shape for suitable at'- tachment to a rotor disc or other member on which it is Secondly, a hollow blade is generally lighter spot welds.

Patented June 14, 19 0 to be mounted. For example, it may beof conventional fir tree form for fitting into a corresponding groove in the rotor disc or other member. In'most cases the root part will have parallel or substantially parallel sides so that it can be inserted endwise into the corresponding groove in the rotor disc or other member. For attachment of the hollow blade part, the root part may have straight parallel grooves formed in opposite sides and the hollow blade part may have straight inturned lips at one end which fit into these grooves, the two parts'being secured together as by welding or brazing.

The root part can be quite small, since it need only project beyond the circumference of the rotor disc or other member by a distance sufficient to accommodate the grooves which receive the inturned lips of the hollow blade par-t. Thus, the weight can be kept low, as compared for instance to that of hollow blades in which the whole of the transition portion is enclosed between two halves of a forged root part.

The invention may be performed in various ways and one particular form of hollow turbine blade embodying the invention, and its method of constructiomwill now be described by way of example with reference to the accompanying. drawings, in which:

Figure 1 shows a partially manipulated sheet metal blank, with some attachments, which will eventually form the hollow blade part;

Figure 2. is a fragmentary longitudinal section through the finished blade showing the root part, the platform part and the transition portion of the hollow blade part, and portions of the platform parts of adjacent blades;

Figure 3 is an exploded view of the pieces which make up the platform part, prior to assembly;

Figure 4 is a perspective View of the blade after assembly but before completion of certain finishing operations; and

Figure 5 is a perspective view of the finished blade.

The hollow turbine blade shown in the drawings is made of three main parts, namely a hollow blade part 10, a root part 1-1 and a platform part 12. The hollow blade part 10 is made from a sheet metal blank by a series of manipulations, i.e., pressing and bending operations, and in its finished form consists of an aerofoil portion 13 and a bifurcated transition portion 14, the transition portion 14 being that portion of the hollow blade part in which the cross-section changes from that of the aerofoil portion to a straight-sided formation where the lower end of the hollow blade part 10 is attached to the root part 11. The finished blade isarranged so that cooling air introduced into the blade through an aperture 16 in the platform part escapes through a series of apertures 23 down the trailing edge 18. These apertures are formed by welding the ends 22 of the teeth 39 of a comb-like element 19 along one edge 20 of the blank as shown in Figure l, and then at a later stage in the manufacture folding the blank to bring the opposite edge 21 adjacent to the edge 20 but on the other side of the teeth of the comb-like element 19, welding this edge 21 to the ends 22 of these teeth, and then severing the exposed part of the comb-like element 19 so as to leave only the tooth ends 22 between the edges 20 and 21 whereby a series of apertures 23 is formed between these tooth ends. After folding, the two flanks of the aerofoil portion are joined together at the tip by The lower portions 14A and 14B of the blank form furcations of thebifurcated transitition portion 14 after folding of the blank. The furcations 14A and 14B of the transition portion 14 have front edges 17a and 17b and rear edges 18a and 18b, respectively.

In the manufacture of the hollow blade part projecting tabs are left which assist in locating the blank during the various manipulations that are performed upon it, these tabs eventually being removed.

The lower end of the hollow blade part is provided with straight intur-ned lips 26 and 27, as best seen in Figure 2. These lips engage corresponding'grooves 40 formed in the root part 11 and are secured to the root part by weld seams 28 and 29 along the exposed edges of the grooves. The intu'rned lips 26 and 27 and the corresponding grooves 40 permit the provision of weld seams '28 and 29 of large cross'sectional area. These weld seams 29 secure the hollow blade part 10 to the root part 11 and also increase the area of contact between these seams and the transition portion 14 of the hollow blade part. They also help to locate the parts 10 and 11 during the welding or brazing operation. Moreover, the portion 34) of the root part that lies above the grooves tends to distribute the centrifugal load so that the hollow blade part 10 will pull more evenly on the weld seams 28 and 29. It is generally convenient to make the root part 11 as a solid forging and then to machine the said grooves and assemble the hollow blade part on to the forging, before machining the root part to provide the required shape for engaging the turbine rotor i.e., before it is given the fir-tree formation shown in Figures 2 and 5.

The platform part is made up of four sheet metal pieces as shown in Figure 3, namely a. front plate or portion 31, a rear plate or portion 32, a side portion 33 which engages the convex side of the blade and a side portion or piece 34 which engages the concave side of the blade. The front and rear pieces 31 and 32 are of roughly cross-shaped form, the horizontal arms of which will fit into corresponding vertical slots 41 and 42, respectively formed in downwardly-extending portions 33, and 34' of the side pieces 33 and 34 respectively so that the four pieces can be assembled into a box-like structure, generally designated B, as shown in Figure 4. Tabs 35 are provided at the front and rear ends of the side portions 33 and 34 which are bent over into the position shown in Figure 4. The purpose of these tabs is to retain lengths of brazing wire 43 in the shallow recesses 44 outside the outer faces of the front and rear plates or portions 31 and 32, and which are visible in Figure 4, for use in a later stage in'the manufacture.

Before assembly of the platform part, projections 36 and 37 are welded on to the front and rear plates or portions 31 and 32 respectively, these projections being required in the finished blade.

When the hollow blade part 10 has been attached to the root part 11 the front and rear platform pieces 31 and 32 are secured to the front and rear ends 11a, 11b, respectively of the root part 11 by spot welding, and the side platform pieces or portions 33 and 34 are then applied so that the platform part is assembled around the transition zone 14 in the manner shown in Figure 4. The plates or portions 31 and 32 thus constitute front and rear walls covering and closing the spaces between the front edges 17a, 17b and rear edges 18a, 18b, respectively, of the furcations 14A and 14B. Brazing Wires 43 are then inserted in the afore-mentioned recesses 44 and are retained there by the lugs 35, and the blade is heated to braze the pieces of the platform part together. As all the pieces'31 to 34 of the platform part are brazed together, the pieces 31 and 32 serve to secure the platform part as a whole to the root part 11.

The blade is then subejcted to machining operations which remove the tabs 35 and any other parts of the side pieces 34 and 35 which still project beyond the front and rear plates or portions 31 and 32 respectively, which also remove the projecting ends of the cross arms 45, 46 of these front and rear pieces, and which reduce the projections 36 and. 37 to the finished dimensions. The root part- IL is also machined into the fir-tree form. A transverse hole 47 is drilled through the transition por tion of the hollow blade part and is lined with a ferrule 38 through which a lacing wire can be inserted before the turbine blades are assembled on the rotor.

When the turbine rotor has been assembled the platform part 12 of this blade abuts with the corresponding platform parts 12' and 127 of adjacent blades as shown in Figure 2, thereby providing a barrier which prevents the hot gases that will pass through the turbine from coming into contact with the transition portion.

What I claim as my invention and desire to secure by Letters Patent is:

1. A hollow blade for a turbine or the like comprising a solid root part shapedto fit into a groove in a member on which said blade is to be mounted and having a front end and a rear end, a hollow blade part made from sheet material attached at one end to saidvroot part and having an aerofoil cross-section for a substantial proportion of its length and a transition portion of varying crosssection between said aerofoil portion and said end attached to saidroot part, and a platform part which fits around said hollow blade part where said aerofoil portion of said hollow blade part joins said transition portion thereof, said platform part having portions extending towards said root part and attached respectively to the front and rear ends of said root part to secure said platform part to said root part, said portions of said platform part also constituting front and rear walls assembled around said transition portion of said hololw blade part.

2. A blade according to claim 1 in which said root part has straight parallel grooves formed in opposite sides thereof and said hollow blade part has straight inturned lips at said end thereof engaging in said grooves, and the attachmentbetween said blade part and said root part comprising weld seams along said grooves securing said hollow blade part to said root part,

3. A blade according to claim 1 in which said platform part is an assembly of four sheet metal elements comprising the two said portions attached to said root part, and two side portions, and means connecting each said side portion to said two first-mentioned portions.

4. A hollow blade for a turbine comprising a solid root part having from and rear ends, a hollow blade part of sheet metal attached at one end to said root part and having an aerofoil portion which extends for a substantial proportion of its length and a bifurcated transition portion of varying cross section at its radially inner end, said bifurcated transition portion including later-a1 furcations each with front and rear edges and formed at their radially inner ends with relatively opposed parallel inturned straight lips, said root part being formed with grooves receiving said lips, said transition portion being open between said front edges and said rear edges of said furcations, and a platform part disposed around said hollow blade at the junction of its transition portion and its portion of'aerofoil cross section, said platform including front and rear plates respectively covering the space between said furcations at said front edges and said rear edges of said furcations, one of said plates having an opening therethrough to permit entry of cooling fluid into said transition section between said furcations, said front and rear plates also being secured against said front and rear ends of said root part respectivelyto fix said platform part thereto.

5. A rotor for a turbine or the like comprising a ring of hollow blades assembled around a hub member, each of said hollow blades comprising a root part having a front end and a rear end and which fits in'a groove in said hub member, a hollow blade part made from sheet material attached at one end to said root part and having an aerofoil cross-section fora substantial proportion of its length and a transition portion of varying cross-section between said aerofoil portion and said end attached to said root part, and a platform part which fits around said hollow blade'part where saidaerofo'il portion of said hollow blade part joins said transition portion thereof, the

shape of said platform part being such that said platform part abuts identical platform parts of adjacent blades assembled on said hub member to form a partition between the blade channels defined by the aerofoil portions of said blades and the transition portions of said blades, said platform part having portions extending towards said root part and attached respectively to said front and rear ends of said root part to secure said platform part thereto and also constituting front and rear walls bounding said transition portion of said hollow blade part.

References Cited in the file of this patent UNITED STATES PATENTS Hirt Sept. 2, 19 19 Sollinger Oct. 20, 1953 Stalker June 5, 1956 Wayne Jan. 14, 1958 FOREIGN PATENTS Germany Oct. 27, 1952 France Apr. 13, 1955 

